The invention concerns an electrical machine, in particular a three-phase generator, according to the preamble of Claim 1.
It is known to use three-phase generators of the generic type, for example in the onboard power supply system in motor vehicles, because of their excellent maintainability, i.e. with few pans subject to wear.
The generator becomes energized by means of a stationary exciter winding which sits on the internal pole. The energizing field then magnetizes the alternately arranged rotating claws of the claw pole rotor system, also called a conductor element rotor. The principle utilized here is that the field coil wound around the internal pole energizes the entire magnetic flux, and conveys it via an air gap to the claw pole rotor system. The rotating claws must be arranged so they are magnetically insulated from, but mechanically joined to, one another.
This join between the claws of the respective magnet wheel halves is accomplished according to the prior art, as described for example in DE-OS 25 48 314, by means of a nonmagnetic ring that lies inside the claws, or by means of a plurality of nonmagnetic ring segment pieces that lie between the claws, the claws being in most cases soldered to these nonmagnetic joining elements. The arrangement of the parts being joined results, however, in solder points which are relatively difficult of access, and, in the case where ring segment pieces are used, also is a plurality of parts to be produced and joined, which makes production of the claw pole rotor complex and expensive. Also worth noting is the fact that the joins between the claws and the nonmagnetic joining elements are exposed, due to the high rotation speed of the claw pole rotor and the resulting centrifugal force, to large stresses, and must be correspondingly well made in order to minimize the risk that a join will pat and thus destroy the entire generator.
Furthermore it has already been proposed, in order to prevent deformation of the claw tips due to centrifugal force loading, to join each claw tip via a nonmagnetic joining element to the claw root, located facing it, of the respective other pole ring. But this solution also does not simplify production.
A further important consideration in the correct operation of generators of the type mentioned above is adequate cooling of the rotor system, which according to the prior art can be an air cooling or liquid cooling system and can be monitored by means of temperature sensors so that if overheating should occur an additional fan can be switched on or generator operation can be halted.
The purpose of the present invention is, among other things, to create an electrical machine in particular a three-phase generator, of the generic type that is as reliable and maintenance-free as possible due to joins of high load capacity between the joining element and the claws, and can nevertheless be constructed using a simple and economical production process. Moreover the dissipation of waste heat in the electrical machine according to the invention is intended to be simple and efficient.
According to the invention, the object is achieved by means of the features indicated in the characterizing portion of claim 1.
The arrangement of the nonmagnetic plate, which serves as joining element, on the surface of the first pole ring facing away from the claws of the first pole ring makes it possible first to assemble the two magnet wheel halves and then to add the plate which joins them (or vice versa), and thereafter to perform all the steps to attach the plate to the two magnet wheel halves in a single operation. Additionally resulting, between tie said surface of the first pole ring and the board, is the advantage of a large joining surface, which also favors the transfer of waste heat from the claw pole rotor to the plate, from which it can easily be dissipated via a conventional cooling system.
Preferably the join between the plate and the magnet wheel halves is made by fusion welding, which results in a highly reliable join.
Advantageously, the claws of the second pole ring are longer than the claws of the first pole ring, and extend into the interstices between the claws of the first pole ring as far as the said surface of the first pole ring. Shortening the claws of the first pole ring increases the centrifugal strength of the claw pole rotor system, since the centrifugal force load on the unattached tips of these claws is reduced. Extending the claws of the second pole ring as far as the said surface of tie first pole ring causes all the joins between the magnet wheel halves and the board to lie in one plane, so that the joining process is further simplified and can readily be automated.
Furthermore, according to the invention the nonmagnetic plate can have at its periphery an annular extension that engages into steps in the tips of the claws of the second pole ring, and in the region of the first pole ring facing away from its claws. This results in accurate, easy positioning of the parts being joined, and the joining surface area is increased.
The magnet wheel halves can be configured as forgings, into which the said steps are machined by lathe-turning. Manufacture of the magnet wheel halves is thus economical, and a precisely manufactured fitting point for the join between the board and the magnet wheel halves can nevertheless be produced. This eliminates the need for continual readjustment of welding parameters, and permits a laser welding process which causes less material distortion than conventional welding.
Preferably a narrow air gap, which allows efficient dissipation of waste heat, is provided between the nonmagnetic plate and the section of the housing running approximately parallel to it.
To reinforce the cooling effect, the nonmagnetic plate can moreover be equipped with orifices through which balance holes can also be made in the claw pole rotor.